Background. The effectiveness of calcium in retarding bone loss in older postmenopausal women is unclear. Earlier work suggested that the women who were most likely to benefit from calcium supplementation were those with low calcium intakes. Methods. We undertook a double-blind, placebo-controlled, randomized trial to determine the effect of calcium on bone loss from the spine, femoral neck, and radius in 301 healthy postmenopausal women, half of whom had a calcium intake lower than 400 mg per day and half an intake of 400 to 650 mg per day. The women received placebo or either calcium carbonate or calcium citrate malate (500 mg of calcium per day) for two years. Results. In women who had undergone menopause five or fewer years earlier, bone loss from the spine was rapid and was not affected by supplementation with calcium. Among the women who had been postmenopausal for six years or more and who were given placebo, bone loss was less rapid in the group with the higher dietary calcium intake. In those with the lower calcium intake, calcium citrate malate prevented bone loss during the two years of the study; its effect was significantly different from that of placebo (P less than 0.05) at the femoral neck (mean change in bone density [+/- SE], 0.87 +/- 1.01 percent vs. -2.11 +/- 0.93 percent), radius (1.05 +/- 0.75 percent vs. -2.33 +/- 0.72 percent), and spine (-0.38 +/- 0.82 percent vs. -2.85 +/- 0.77 percent). Calcium carbonate maintained bone density at the femoral neck (mean change in bone density, 0.08 +/- 0.98 percent) and radius (0.24 +/- 0.70 percent) but not the spine (-2.54 +/- 0.85 percent). Among the women who had been postmenopausal for six years or more and who had the higher calcium intake, those in all three treatment groups maintained bone density at the hip and radius and lost bone from the spine. Conclusions. Healthy older postmenopausal women with a daily calcium intake of less than 400 mg can significantly reduce bone loss by increasing their calcium intake to 800 mg per day. At the dose we tested, supplementation with calcium citrate malate was more effective than supplementation with calcium carbonate.
Bone mineral content (BMC) and bone mineral density (BMD) of the spine (L2-L4) and hip (at femoral neck, Ward's triangle, and greater trochanter sites) were determined by dual-photon absorptiometry (DPA), and of the radius by single-photon absorptiometry (SPA) in healthy postmenopausal women aged 40-70 years. The relationships of BMC and BMD to years since menopause were examined separately in 97 women who were above 115% of ideal body weight (IBW) and in 128 women below. The heavier women had significantly greater mean BMC and BMD at each site than did the normal-weight women. In the normal-weight women, there was a significant negative correlation between BMD and years since menopause at each measurement site except the greater trochanter. In the obese women, BMD decreased with increasing years since menopause at the radius site only and BMC declined with increasing years after menopause at the hip (femoral neck and Ward's triangle region) as well as the radius. Thus, body size is a significant determinant of BMD in this population. The pattern of loss of BMD from Ward's triangle and femoral neck regions of hip are similar to that of the spine. The BMC and BMD findings in the hip suggest that remodeling occurs at this weight-bearing site which has a favorable effect on bone strength.
Dual photon absorptiometry measurements of the spine are subject to drift associated with source, source strength, and truncal thickness. This study was conducted to determine the extent to which this drift in bone mineral density (BMD) measurements can be improved by analysis of scans with a new software version, 08C, and by applying external standard or phantom corrections to scans analyzed with the older version, 08B. A phantom, consisting of human lumbar vertebrae embedded in acrylic, and five clear acrylic plates to simulate a soft-tissue thickness range of 15.2-27.9 cm, was measured on a Lunar Radiation Corp DP3 scanner over the life of a 153-gadolinium (Gd) source and scans analyzed with software versions 08B and 08C. Phantom BMD was lower with 08C at both high [0.012 +/- 0.002 (SEM) g/cm2, P less than 0.001] and low (0.027 +/- 0.003 g/cm2, P less than 0.001) count rates than with 08B. Phantom BMD of scans analyzed with 08B increased with increasing source age and the source strength-related increment increased significantly as acrylic thickness increased (P = 0.014). When the same scans were analyzed with 08C, the thickness-related effect was corrected whereas a small (0.011 g/cm2/year) source-strength effect persisted. The effects of source strength and truncal thickness on BMD were also evaluated in 40 humans scanned at two detector collimations to vary count rate. With 08B, mean BMD was 1% greater when measured with 8 than with 13 mm collimation (mean difference 0.011 +/- 0.003 g/cm2, P = 0.001), whereas the version 08C, mean BMD was the same at the two collimations.(ABSTRACT TRUNCATED AT 250 WORDS)
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